Most present-day, electronic, semiconductor devices measure and manipulate electron charge. Recently, however, there has been considerable interest in semiconductor devices that measure and manipulate the spin of electrons, either alone or in conjunction with electron charges.
A number of devices are envisioned using electron spin, including Spin-FETs (Field Effect Transistors), Spin-LEDs (Light Emitting Diodes) and Spin-RTDs (Resonant Tunneling Devices), optical switches, modulators, encoders, decoders and quantum bits for quantum computation and communication. An overview of electronic devices based on electron spin is provided in S. A. Wolf, et. al., “Spintronics: A Spin-Based Electronics Vision for the Future”, Science, Vol. 294, pps. 1488-1495, (November 2001).
Ferromagnetic semiconductors such as GaMnAs and InMnAs are possible candidates for the ferromagnetic film that may be used in electron spin devices. Unfortunately, to date, the highest Curie temperature (the temperature beyond which ferromagnetic properties disappear) for GaMnAs is 110K which is too low for routine semiconductor device applications.
Gallium nitride, p-doped with five percent manganese, has been predicted to have a Curie temperature above room temperature. However, this concentration of five percent is several orders of magnitude higher than the solubility limit of manganese in gallium nitride. The low solubility results in the formation of stable secondary phases, such as GaMn and Mn3N2. Recently, there have been reports of ferromagnetic ordering in gallium nitride n-doped with manganese. Nevertheless, phase segregation is still a problem.
In such phase segregation, the manganese migrates into strips and clusters in the film leaving the remaining areas depleted of manganese. An inability to provide for a uniform film is an obstacle to the production of electronic devices described above.
Current investigations in the growth of GaMnN use low temperature molecular beam epitaxy to suppress the formation of intermediate compounds such as Mn3N2 and GaMn.